This application claims the benefit of French Application No. 00 07372 filed Jun. 8, 2000.
The present invention relates to a projection screen of retractable type, adapted to be used in an extended position in combination with a projector, in particular a video projector, and with a sound broadcasting device.
More precisely, a screen according to the present invention is retracted when not in use, in order both to make it less cumbersome and to avoid the risk of its becoming dirtied and/or deteriorated.
Furthermore, a screen according to the present invention is of the type known as acoustically transparent, which is to say that it is permeable to sound waves.
This makes it possible to implement simultaneously the projection of video together with sound broadcasting coming from sound sources placed behind the acoustically transparent screen.
The advantage of placing the sound sources behind the screen has been known since the existence of film with sound, known as xe2x80x9ctalking picturesxe2x80x9d. This is to procure the sensation of coherence between the projected image and the sound diffused for the spectator.
The simultaneous implementation of sound sources and an acoustically transparent video screen makes it possible to reproduce this sensation in a smaller environment, in particular a domestic environment.
Video screens combining the features mentioned above are known. Conventionally, such screens are formed from a sheet of plastics material, generally PVC, perforated with orifices of small size adapted to let through sound waves.
Such screens are formed from a sheet of PVC of which the perforations typically represent between 2% and 6% of their surface and let the sound through only very imperfectly. A large part of the sound is reflected, instead of passing though the orifices that perforate the screen. This phenomenon causes substantial attenuation of the sound level, particularly at high frequencies. Furthermore, the multiple reflections created initially by the full portions of the screen cause aberrations in the acoustic response, resulting in irregularities in the transfer function and in distortions that degrade the sound quality.
In addition, in an environment that is more restricted than a conventional movie theater, the spectator is normally placed much closer to the screen. The perforations of the screen, closer than a certain distance, become visible, and add a raster effect to the image that is bothersome.
Such screens are in general retractable through rolling onto a cylinder rotated by a motor, and frequent repetition of this operation gives rise to deformation either on the edges of the screen, or on the median part. This arises from the fact that screens that can be rolled up are not generally tensioned by the edges, but only by a weighting bar, that applies a vertical stretching force to the screen, towards the bottom.
With time, the material making up the screen can stretch in an uneven manner, thereby giving rise to deformations that risk impairing the flatness of the screen. Apart from the aesthetic drawbacks that this implies, the focusing of the projector is altered, thereby altering the quality of the image in certain zones. This defect is worse if acoustically transparent screens having perforations are used.
Many devices exist for tensioning the edges of screens that roll up, but they are generally both costly and unaesthetic, and can also jam due to wear. The object of the present invention is to provide an acoustically transparent retractable screen without the drawbacks mentioned above.
The present invention relates to a retractable projection screen that is transparent to sound waves that has at least two layers of white fabric superimposed and joined together.
According to a first embodiment of the present invention, the screen with at least two layers of superimposed fabric is rolled onto a rolling-up device having a weighting bar which is of sufficient weight for stretching the fabric so that the stretching compensates for the difference in diameter between the two layers when they are rolled up.
This makes it possible to avoid the formation of a fold in the inner layer of fabric, when the screen is rolled up.
According to a second embodiment of the present invention, the screen folds into a plurality of rectangles linked by folds when the weighting bar rises under the effect of traction devices that are applied to it.
According to a third embodiment of the present invention, a piece of fabric forming the screen is fixed by one edge defining a first end, an opposite end being affixed to a rolling-up device having a roller disposed in a fixed manner parallel to the first end, a mobile roller serving as a weighting bar being interposed between the two ends so as to tension the fabric towards the bottom by gravity. The roller is fixed to pressing members that tend to make contact between two layers of fabric which are thus disposed back to back.
Preferably the rolling-up device enables the simultaneous retraction of a sound broadcasting device in such a manner that the device is situated substantially at mid-height behind the screen when the latter is in the extended position.
The features and advantages of the present invention will be better understood after reading the following detailed description with reference to the accompanying drawings.